The invention concerns a belt retractor for a seat belt. If, for example, a child is buckled-up with a seat belt in a motor vehicle, there is the risk of the child playfully pulling the belt out of the belt retractor during the journey and thereby extending the entire length of the belt which is available; this may have an adverse effect on the safety retaining function of the seat belt or even render it completely ineffective.
Even adults may sometimes pull the belt out during the journey farrther than is permissible for ensuring the required safety, for example to increase the comfort while traveling.
With regard to this problem, U.S. Pat. No. 5,518,197 discloses a belt retractor for a seat belt which permits an automatic locking retractor (“ALR”) mode. An ALR mode is understood to be a manner of operating the belt retractor, in which, after the vehicle occupant to be secured has put on the seat belt, the seat belt is prevented from being pulled out. For this purpose, the previously known belt retractor has an eccentric disc which is connected in a rotationally fixed manner to the belt reel of the belt retractor and drives a cam disc directly. The cam disc and the eccentric disc form a wobble gear which is designed as a step-down gear.
In addition, the previously known belt retractor has a blocking pawl which, in a blocking position (i.e., in the activated state) blocks a tooth ratchet wheel (which rotates at the same time as the belt reel of the belt retractor) in the belt pull-out direction of rotation of the seat belt and, in a release position (i.e., in the inactive state) leaves the toothed ratchet wheel unaffected because it is disengaged from the toothed ratchet wheel.
In the case of the previously known belt retractor, the cam disc is configured in such a manner that it can switch the blocking pawl from the release position into the blocking position and conversely from the blocking position into the release position. If the blocking pawl is situated in its blocking position, then the previously known belt retractor is operated in the ALR mode because the blocking pawl is namely in engagement with the toothed ratchet wheel and thereby blocks the seat belt from being pulled out in the pull-out direction. If, in contrast, the blocking pawl is in its release position, then the blocking pawl and the toothed ratchet wheel are disengaged and the belt retractor can be operated in the usual manner. In this case, a usual operation of the seat belt retractor is understood to mean that, even after having been put on, the seat belt can still be pulled out as long as the pulling-out takes place relatively slowly; the usual manner of operation is also referred to as an emergency locking retractor (“ELR”) mode.
In the case of the previously known belt retractor, for satisfactory functioning it is necessary for the entire length of the seat belt to be matched relatively precisely to the step-down ratio of the step-down gear; this is because only if the length of the seat belt is matched relatively precisely to the transmission ratio or step-down ratio it is ensured that, after the blocking pawl is deactivated by the cam disc, it is not re-activated unintentionally. In the case of the previously known belt retractor, the switching points are, therefore, fixedly predetermined by the step-down ratio of the step-down gear.